VECTOR MODULATOR DESIGN, PART 2 - MMIC CIRCUITS ENABLE DIRECT-CARRIERMODULATION

CONVENTIONAL microwave transmitter designs are based on modulation at the intermediate frequency (IF), requiring a complex chain of mixers, filters, and amplifiers to upconvert the modulated signal to the trans mission frequency. By applying direct modulation of the microwave carr ier signal, a significant reduction in system hardware requirements is achieved. A single-chip transmitter design for indoor radio communica tions provides direct-carrier modulation in the 17/18-GHz frequency ra nge, employing a microwave-monolithic-integrated-circuit (MMIC) phase shifter and variable attenuator to provide phase and amplitude control . This second part of a two-part article presents the physical realiza tion of the phase-and amplitude-control circuits-which are implemented with a voltage-controlled oscillator (VCO) and 360-deg, phase shifter on one chip and an amplitude modulator on a separate chip. The struct ure and performance of the balanced vector modulator (which is realize d by cascading two amplitude biphase modulators) will also be describe d.